1. Field of the Invention
The present invention is generally related to a marine propulsion engine and, more particularly, to a marine propulsion engine with a cooling system in which conductivity sensors are used to detect the presence of water at specifically chosen locations within the cooling system to assure that the cooling system is properly drained so that potential freezing water damage can be avoided.
2. Description of the Prior Art
Marine propulsion devices often have cooling systems that require the water to occasionally be drained from the cooling system. This is particularly true when is the marine vessel is stored during winter months. If the water within the cooling system is not properly drained, freezing can cause severe damage to the engine of the marine propulsion device. This is particularly true in marine vessels that utilize a sterndrive or inboard propulsion system. An internal combustion engine, which is located within the marine vessel, is typically provided with a plurality of cavities within the engine block to circulate cooling water in thermal communication with the heat producing portions of the engine, such as the cylinders and combustion chambers. In addition, numerous hoses and other conduits are associated with the engine to facilitate the flow of cooling water through the various portions of the engine that are in thermal communication with the combustion chambers. When the marine vessel is stored over the winter months, it is necessary that all of the water be removed from the cooling system to avoid the potentially serious damage that can be caused if the water within the cooling system freezes.
U.S. Pat. No. 5,628,285, which issued to Logan et al on May 13, 1997, discloses a drain valve for a marine engine. The drain valve assembly is used for automatically draining water from a cooling system of an inboard marine engine when the ambient temperature drops to a preselected value. The drain valve includes a cup-shaped base having a group of inlets connected to portions of a cooling system of the engine to be drained, and the open end of the base in enclosed by a cover. Each inlet defines a valve seat and a sealing piston is mounted for movement in the base and includes a series of valve members that are adapted to engage the valve seats. An outlet is provided in the side wall of the cup-shaped base. The valve members on the sealing piston are biased to a closed position by a coil spring and a temperature responsive element interconnects the sealing piston with the cover. The temperature responsive element is characterized by the ability to exert a force in excess of the spring force of the coil spring when the ambient temperature is above approximately 50 degree F., to thereby maintain the valve member in the closed position. When the temperature falls below the selected temperature, the temperature responsive element will retract, thereby permitting the valve members to be opened under the influence of the spring to automatically drain water from the cooling system of the engine.
U.S. patent application Ser. No. 09/400,675 (M09334) which was filed by Logan et al on Sep. 21, 1999, and assigned to the assignee of the present application, discloses an engine cooling system that is provided with a manifold that is located below the lowest point of the cooling system of the engine. The manifold is connected to the cooling system of the engine, a water pump, a circulation pump, the exhaust manifolds of the engine, and a drain conduit through which all of the water can be drained from the engine.
U.S. Pat. No. 3,873,927, which issued to Overall et al on Mar. 25, 1975, describes a system for detecting wet and icy surface conditions. The system is intended to detect wet and icy conditions on the surface of highways, airport runways, and the like. A first capacitor is positioned on a surface the condition of which is being detected. This capacitor has first and second spaced apart electrodes which are positioned substantially coplanar with the surface and exposed to atmospheric precipitation which affects the capacitor's dielectric and capacitance characteristics. A second capacitor having first and second spaced apart electrodes is positioned so as not to be exposed to atmospheric precipitation. Respective out-of-phase time varying signals are applied to the first electrodes of the capacitors and the second electrodes are commonly connected. The system further includes a conductivity sensor having a first and second spaced apart electrodes exposed to atmospheric precipitation which affects the sensor's resistance, a sensor circuit which supplies an output voltage the magnitude of which is a function of the resistance of the sensor, and a logic circuit responsive to any signal coupled to the second electrodes of the capacitors reaching a predetermined precipitation threshold magnitude and to the output voltage of the sensor circuit reaching a predetermined ice threshold magnitude to provide an output which indicates an icy surface condition.
U.S. Pat. No. 5,474,261, which issued to Stolarczyk et al on Dec. 12, 1995, describes an ice detection apparatus for transportation safety. One embodiment of the invention is an ice detection system that comprises a network of thin, flexible microstrip antennas distributed on an aircraft wing at critical points and multiplexed into a microcomputer. Each sensor antenna and associated electronics measures the unique electrical properties of compounds that accumulate on the wing surface over the sensor. The electronics include provisions for sensor fusion wherein thermocouple and acoustic data values are measured. A microcomputer processes the information and can discern the presence of ice, water frost, ethylene-glycol or slush. A program executing in the microcomputer can recognize each compound's characteristic signal and can calculate the compound's thicknesses and can predict how quickly the substance is progressing toward icing conditions. A flight deck readout enables a pilot or ground crew to be informed as to whether deicing procedures are necessary and/or how soon deicing may be necessary.
U.S. Pat. No. 5,970,428, which issued to Brennan on Oct. 19, 1999, describes a ground loop detector circuit and method. The circuit and method for an instrument that is used with either a pH sensor or a conductivity sensor is disclosed. In the instrument used with a pH sensor, an AC diagnostic signal is provided to the sensor. A high input impedance diagnostic signal monitor monitors the voltage at a node adjacent the output of the diagnostic signal source. The occurrence of a ground loop causes the voltage at the node to drop. The instrument used with the conductivity sensor, not only monitors current returning to the diagnostic circuitry from the sensor but also uses a high input impedance monitor to monitor the current leaving the diagnostic circuit to the sensor. The relationship between the current from the sensor and the current to the sensor can be used to determine if a ground loop has occurred as such a loop will cause the current from the sensor to be less than the current to the sensor.
When the operator or owner of a marine vessel drains the cooling system of the engine, it is difficult for the operator to be sure that all of the water has been removed. If any of the water is left remaining within the cavities of the engine block or within other conduits of the cooling system, that remaining water can possibly freeze and result in serious damage to the marine propulsion system. It would therefore be significantly beneficial if a system could be provided which informs the operator of the presence or absence of water within critical locations of the cooling system following a draining procedure. It would also be significantly beneficial if signals could be provided to the operator to annunciate the presence or absence of water at these critical locations within the cooling system.